The microstructure of soils (the arrangement of pores and voids, aggregation and surface characteristics of particles) is substantially modified by freezing. Soils so modified differ, in a number of important properties, from soils not previously frozen. Furthermore, each time a soil is frozen there is a redistribution of particles, moisture and solutes. Corrosion of buried pipes is known to be related to the ground conditions. Accordingly the particular nature of frozen ground needs

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... on in this respect. Studies of microstructure o f samples of freezing, frozen and unfrozen soils, many obtained from a full-scale experimental study of the effects o f freezing on a buried pipeline, have provided an explanation for measured changes in bulk geotechnical properties of the materials. The microstructure viewed by optical microscopy, reveals the soil structure as having a complex and striking dependence on freezing history. Scanning electron microscopy shows further details in clay rich soils. Freezing at tem peratures occurring in nature normally does not convert all the soil w ater to ice. The effects of particle surface forces is to reduce the freezing point of the w ater nearest a mineral surface. The distribution of solutes is radically altered, with pockets of high concentration interconnected by a liquid phase of varying concentration. A variety o f other effects, relating to chemical and mechanical properties o f soils subjected to freezing, have been demonstrated or can be postulated. Some o f these are important in corrosion phenomena. The stresses that have been shown to occur in a pipe as a result o f frost heave in the freezing soil, will also tend to increase the possibility of stress corrosion cracking.